docs: clarify --prune scope for streamlit deploy

[afeld]

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Changes description

snow streamlit deploy --prune help text says "Delete files that exist in the stage, but not in the local filesystem." This is ambiguous — it implies the entire stage is pruned, when in fact pruning is scoped to the individual app's subdirectory (@<stage>/<app-name>/) … as far as I can tell. I used Cortex Code to inspect the code paths, and here was its explanation:

Each app gets its own subdirectory within the shared streamlit stage, and --prune is scoped to that
subdirectory. Here's the chain:

Default stage path per app (streamlit_entity.py):

stage_root = f"{self.model.stage}/{name}"
# → @streamlit/ccs_dashboard/
# → @streamlit/cr_timeliness/
# → @streamlit/mso_waitlist/

--prune scope (api/entities/utils.py → stage/diff.py):

remote_files = stage_manager.list_files(stage_path.full_path)
# LIST @streamlit/ccs_dashboard  ← never sees other apps' files

Deletions are also scoped to that same prefix, so app_b/ files are never listed, compared, or deleted
when deploying app_a.

Bottom line: Your three apps are isolated by subdirectory, so --prune won't clobber them. My original
answer was correct, just for the wrong stated reason — it's not a dedicated stage per app, it's a
dedicated subdirectory within the shared streamlit stage.

Slightly difficult to troubleshoot, so would love verification on this.

This matters when multiple apps share the same default streamlit stage: users may avoid --prune unnecessarily, fearing it will delete other apps' files.

There could/should be tests for this, but to be honest, I don't have time to dig into that.

Thanks!